The invention relates generally to electrochemical cells, batteries in particular, and specifically to improved cathode materials therefor. The cathodes are particularly intended for use in implantation in the human body to operate electrical devices such as cardiac pacemakers and the like. However, other applications such as in small cells for low current drain use generally are also within the purview of this invention.
The invention is of specific interest in connection with batteries, such as lithium anode batteries, incorporating iodine-complex cathodes. Such cathodes have also been referred to as iodine-containing charge-transfer compounds. Charge-transfer compounds are sometimes referred to as complexes and sometimes as donor-acceptor compounds. The iodine in such a cathode reacts electrochemically with the battery anode, lithium for example, to provide an electrical current. This reaction causes an iodide electrolyte to form in situ between the anode and cathode. The charge-transfer donor typically used has been a polyvinylpyridine such as poly-2-vinylpyridine or poly-4-vinylpyridine. U.S. Pat. Nos. 3,660,163 to Moser, 3,660,164 to Hermann et al and 3,674,562 to Schneider et al describe examples of such batteries.
In these kinds of batteries, it has been determined that additional amounts of free iodine, i.e., excess iodine which is in a substantially separate phase from the charge-transfer donor, may be included as part of the cathode material to provide an iodine "reservoir" for the battery to draw on during discharge. The additional iodine increases the useful life of the battery.